Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $88.78   5.205%   $93.401   $93.40   $93.40   $93.40  
  Purchase #2 $178.61   7.368%   $191.77   $191.77   $191.75   $191.80  
  Purchase #3 $183.72   10.816%   $203.5912   $203.59   $203.60   $203.60  
  Purchase #4 $238.62   12.114%   $267.5264   $267.53   $267.55   $267.50  
  Purchase #5 $160.83   6.720%   $171.6378   $171.64   $171.65   $171.60  
  Purchase #6 $123.93   13.378%   $140.5094   $140.51   $140.50   $140.50  
  Purchase #7 $152.47   10.211%   $168.0387   $168.04   $168.05   $168.00  
  7 purchase totals = $1,126.96       $1,236.4745   $1,236.48   $1,236.50   $1,236.40